1. Field of the Invention
The present invention relates to oil-filled protectors for use with electric motors and, more particularly, oil-filled protectors for use with electric motors used with electric submergible pumps that are suspended within wellbores.
2. Setting of the Invention
Electric submergible pumps (ESP's) are widely used throughout the world for recovering subterranean fluids to the earth's surface. For the long term successful operation of such ESP's, the electric motor must be supplied with uncontaminated, cooling motor oil. Unfortunately, it has been found that the motor oil can become contaminated over time by wellbore fluids. This contamination can lead to shortened operational life, which in turn will cause the premature shutting-in of the wellbore, and the costly removal and repair of the ESP.
Specifically, the electric motors used in ESP's will almost always include an oil-filled motor protector to permit the expansion and contraction of the motor oil, and which are sealed to prevent wellbore fluids from contaminating the motor oil used to cool the electric motor. One important feature found in most such protectors is a one-way acting pressure relief valve, which allows motor oil to be vented out from the internal expandable chambers if the motor oil expansion cannot be accommodated when the temperature of the motor oil increases during operation. Usually, the motor oil is vented to a cavity or internal section of the protector that is filled with clean motor oil. However, despite numerous arrangements to prevent wellbore fluid contamination of the motor oil, over time, wellbore fluids leak into, and displace the oil and eventually fill this section. One prior arrangement to prevent wellbore fluids from contaminating the motor oil is shown in U.S. Pat. No. 4,421,999, which discloses a U-shaped tube connected to the intake of the pressure relief valve.
If wellbore fluids come into contact with the pressure relief valve, the valve itself may be damaged because wellbore fluids contain chemicals and suspended solids. When these wellbore fluids come into contact with the pressure relief valve, elastomeric O-ring seal(s) used therein can be chemically destroyed thereby causing a gap to be formed in the seal so that wellbore fluid can by-pass the valve and enter the interior of the protector. Also, upon the opening of the pressure relief valve, the suspended solids can become trapped between the valve seat and the valve's poppet or the ball so that the pressure relief valve will not fully close, resulting in wellbore fluids being able to leak past the pressure relief valve.
There is a need for a simple, efficient, and inexpensive mechanism to inhibit or preferably prevent wellbore fluids that enter the normally oil-filled section in the motor protector from coming into contact with the pressure relief valve, and thereby ensure the desired long term operational life of the ESP.